Resilience in Function, Microbial Community Structure,and Nitrifier Composition of Bench-Scale Biofilm Reactors during WetWeather Disturbances

Wet weather events, such as hurricanes and tropical storms, are on the rise globally due to climate change. Activated sludge systems are vulnerable to wet weather, as hydraulic overloading can cause a washout of biomass. Biofilm-based treatment technologies, such as moving bed biofilm reactors (MBBR), can improve resiliency by preventing biomass washout and protecting slow-growing nitrifiers. In this study, we investigated the resilience of a biofilm system challenged by wet weather events and examined the impact of different disturbances on the system’s microbial community. We performed three simulated wet weather stressor experiments on replicate bench-scale MBBR bench reactors: (1) high flow and high load (representative of flooding and a first flush); (2) high flow, high load, and no dissolved oxygen (DO) (representative of flooding with power outage); and (3) starvation and no DO (temporary plant shut down). The biofilm system’s function, in terms of ammonia-N and soluble organic carbon removal, was resilient to the wet weather disturbances as the function recovered to the baseline performance after disturbance within hours. The biofilm microbial community structure was resistant (not impacted by the disturbance), and the nitrifier community was resilient (the ability to recover to baseline conditions after the disturbance).